Field of the Invention and Related Art Statement
The present invention relates to an apparatus for displaying ultrasonic images taken by an ultrasonic microscope in which a specimen is scanned two-dimensionally by a focused spot of an ultrasonic beam.
FIG. 1 shows a principal construction of a known ultrasonic microscope. A control unit 1 sends a control signal to a high frequency wave transmitting unit 2 to generate a high frequency burst signal in synchronism with the control signal. The high frequency burst signal generated from the transmitting unit 2 is supplied to a piezo electric transducer 4 via a circulator 3 and is converted into an ultrasonic wave. The ultrasonic wave is focused by an acoustic lens 5 an is projected via an ultrasonic wave propagating medium 6 such as water onto a specimen 7 as a fine spot. The ultrasonic wave thus projected upon the specimen 7 is reflected in accordance with acoustic characteristics of the specimen. The reflected ultrasonic wave is received by the acoustic lens 5 and is converted into an electric signal by the piezo electric transducer 4. The electric signal thus converted is supplied to a receiving unit 8 via the circulator 3. The electric signal is gated in the receiving unit 8 by means of a gate signal supplied from the control unit 1, so that unnecessary signals are removed from the electric signal. Then the electric signal thus gated is amplified and rectified to produce a rectified output signal having an amplitude representing a strength of the reflected ultrasonic wave. The rectified output signal thus obtained is supplied to a scan converter 11 to which are also supplied X and Y direction information signals relating to a scanning position on the specimen 7 and supplied from X direction scanner 9 and Y direction scanner 10, respectively. In the scan converter 11, the rectified output signal is stored as an amplitude signal. Then the amplitude signal is read out and converted into a video signal which is supplied to a display unit 12 such as a cathode ray tube monitor to display an ultrasonic image of the specimen. The X and Y direction scanners 9 and 10 are driven by control signals supplied from the control unit 1 and the acoustic lens 5 is vibrated in the X direction at a high speed by means of the X direction scanner 9 and a specimen table 13 is moved slowly in the Y direction by means of the Y direction scanner 10 so as to effect the two-dimensional scanning.
In the ultrasonic microscope explained above, a single ultrasonic image is obtained by scanning the specimen 7 within a given area, while a distance in the Z direction between the acoustic lens 5 and specimen 7 remains constant. Therefore, when the distance in the Z direction is successively changed in a stepwise manner, a plurality of ultrasonic images representing images of the specimen on different scanning planes at different depths are obtained successively. Therefore, when the ultrasonic lens 5 and specimen 7 are moved relatively to each other in the Z direction by a small pitch distance in a stepwise manner, there are obtained a large number of ultrasonic images and therefore, an inside construction of the specimen 7 can be inspected much more precisely and very small cracks can be found without fail.
Usually the ultrasonic image of the specimen is displayed on a monitor such as a cathode ray tube (CRT) or is recorded on a photographic film. Thus, when a resolution in the Z direction is increased by moving the acoustic lens and specimen relative to each other in the Z direction at a small pitch distance, there are obtained a large number of ultrasonic images. When the specimen is made of materials having uniform characteristics, similar ultrasonic images have to be compared with each other. This results in that small defects or cracks might not be detected. Particularly, in case of displaying ultrasonic images on a single CRT successively, only remarkable changes could be practically detected, because visual images are soon forgotten.
Contrary to this, in case of using the photographic records, it is possible to compare successive ultrasonic images in detail. However, since a great large number of photographic records have to be prepared, the running cost becomes expensive.